Add many missing tests for lines without test coverage

[bmish]

Used nyc/istanbul to identify lines that were missing test coverage. This addresses many but not all of them.

Improved test coverage will make future refactorings safer to perform.

Before:

--------------------------------------------------------|----------|----------|----------|----------|-------------------|
File                                                    |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
--------------------------------------------------------|----------|----------|----------|----------|-------------------|
All files                                               |    97.77 |    95.17 |    99.24 |    97.73 |                   |

After:

--------------------------------------------------------|----------|----------|----------|----------|-------------------|
File                                                    |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
--------------------------------------------------------|----------|----------|----------|----------|-------------------|
All files                                               |    98.37 |    96.45 |    99.43 |    98.34 |                   |

Follow-up to: #505